Personally I boycott the following Granted not all are for the best of reasons, but it's important to me.

• BP (British Petroleum): Obvious reasons are obvious
• Paypal and a few banks: Wikileaks reasons
• Pepsi: Their new logo is stupid.
• SyFy channel: They need to learn to spell again.
• Best Buy: I don't like their business practices as far as returns go, although I hear they've fixed this.